In the description of the background that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
The term “nanostructure” material is used by those familiar with the art to designate materials including nanoparticles such as C60 fullerenes, fullerene-type concentric graphitic particles, metal, compound semiconductors such as CdSe, InP; nanowires/nanorods such as Si, Ge, SiOx, GeOx, or nanotubes single or multi-walled composed of either single or multiple elements such as carbon, BxNy, CxByNz, MoS2, and WS2. One of the common features of nanostructure materials is their basic building blocks. A single nanoparticle or a carbon nanotube has a dimension that is less than 500 nm at least in one direction. These types of materials have been shown to exhibit certain properties that have raised interest in a variety of applications and processes.
U.S. Pat. Nos. 6,280,697 and 6,422,450 to Zhou et al. (both entitled “Nanotube-Based High Energy Material and Method”), the disclosures of which are incorporated herein by reference, in their entirety, disclose the fabrication of carbon-based nanotube materials and their use as a battery electrode material.
U.S. Pat. No. 6,630,772 entitled “Device Comprising Carbon Nanotube Field Emitter Structure and Process for Forming Device”, the disclosure of which is incorporated herein by reference, in its entirety, discloses a carbon nanotube-based electron emitter structure.
U.S. patent application Ser. No. 09/351,537 entitled “Device Comprising Thin Film Carbon Nanotube Electron Field Emitter Structure”, the disclosure of which is incorporated herein by reference, in its entirety, discloses a carbon-nanotube field emitter structure having a high emitted current density.
U.S. Pat. No. 6,277,318 to Bower et al. (entitled “Method for Fabrication of Patterned Carbon Nanotube Films”), the disclosure of which is incorporated herein by reference, in its entirety, discloses a method of fabricating adherent, patterned carbon nanotube films onto a substrate.
U.S. Pat. No. 6,334,939 (entitled “Nanostructure-Based High Energy Material and Method”), the disclosure of which is incorporated herein by reference, in its entirety, discloses a nanostructure alloy with alkali metal as one of the components. Such materials are described as being useful in certain battery applications.
U.S. Pat. No. 6,553,096 entitled “X-Ray Generating Mechanism Using Electron Field Emission Cathode”, the disclosure of which is incorporated herein by reference, in its entirety, discloses an X-ray generating device incorporating a nanostructure-containing material.
U.S. Published Patent Application No. US 2002/0140336 (entitled “Coated Electrode With Enhanced Electron Emission And Ignition Characteristics”), the disclosure of which is incorporated herein by reference, in its entirety, discloses an electrode including a first electrode material, an adhesion-promoter, and a carbon nanotube-containing material disposed on at least a portion of the adhesion promoting layer, as well as associated devices incorporating such an electrode.
U.S. Pat. No. 6,787,122 entitled “Method of Making Nanotube-Based Material With Enhanced Field Emission”, the disclosure of which is incorporated herein by reference, in its entirety, discloses a technique for introducing a foreign species into the nanotube-based material in order to improve the properties thereof.
U.S. Pat. No. 6,876,274 entitled “Large-Area Individually Addressable Multi-Beam X-Ray System and Method of Forming Same”, the disclosure of which is incorporated herein by reference, in its entirety, discloses a structure to generate x-rays having a plurality of stationary and individually electrically addressable field emissive electron sources, such as carbon nanotubes.
U.S. Patent Application No. 2003/0180472 entitled “Method for Assembling Nanoobjects”, the disclosure of which is incorporated herein by reference, in its entirety, discloses a technique for the self assembly of a macroscopic structure with preformed nanoobjects, which may be processed to render a desired aspect ratio and chemical functionality.
U.S. Patent Application Publication No. 2004/0173378 entitled “Methods for Assembly of Nanostructure-Containing Materials and Related Articles”, the disclosure of which is incorporated herein by reference, in its entirety, describes various electrophoretic-type methods for assembling and attaching nanostructure-containing materials to various objects.
As evidenced by the above, nanostructure materials, especially carbon nanotubes and other nanoobjects having a large aspect ratio (that is, a length that is substantially larger than its diameter), possess promising properties that make them attractive for a variety of applications, such as lighting elements, field emission devices such as flat panel displays, gas discharge tubes for over voltage protection, x-ray generating devices, small conduction wires, sensors, actuators and high resolution probes such as those used in scanning microscopes.
The effective incorporation of nanostructure materials into devices has been hindered by difficulties encountered in the processing of the materials. For example, nanostructured materials can be formed by techniques including laser ablation, arc discharge methods, solution synthesis, chemical etching, molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and the like. Each of these techniques to assemble the nanostructure materials present their own challenges.
Post-formation methods including screen printing and spraying have been utilized to deposit pre-formed nanoobjects, such as carbon nanotubes, on a substrate. These techniques pose drawbacks as well. For example, screen printing can require the use of binder materials as well as an activation step, which can result in a relatively low-resolution deposition of material. Spraying can be inefficient and often is not practical for large-scale fabrication. Moreover, screen printing and spraying can result in the nanostructure materials being randomly distributed on the substrate.
Carbon nanotubes have been grown directly upon substrates using of CVD techniques. See, for example, J. Hafner et al., Nature, Vol. 398, pg. 761, 1999; U.S. Pat. No. 6,457,350; and U.S. Pat. No. 6,401,526. One potential application of this technique is the formation of conducting wires made from nanostructure materials, such as electrical circuitry comprised of carbon nanotubes. The CVD process can be used to form the carbon nanotubes that can then be attached to electrodes at specific locations using CVD techniques to form the conducting wires. These techniques can require reactive environments at relatively high temperatures (for example, about 600° C.–1,000° C.) and the use of catalysts to effectively grow the nanotubes. The requirement for such harsh environmental conditions severely limits the types of substrate materials that can be utilized. In addition, the CVD technique often results in multi-walled carbon nanotubes. These multi-walled carbon nanotubes generally do not have the same level of structural perfection as single-walled nanotubes, and thus can have inferior electronic emission properties when compared to single-walled carbon nanotubes.
Other fabrication techniques involving nanostructured materials include precisely controlling the deposition of individual or small groups of nanoobjects, such as carbon nanotubes, onto a substrate to form sharp tips or projections. See, for example, Dai, Nature, Vol. 384, pgs. 147–150 (1996); and R. Stevens et al., Appl. Phys. Lett., Vol. 77, pg. 3453, 2000. These techniques can be challenging to carry out in a large-scale production or batch process.